Dispersion of fine particles of modified polyethylene and process for preparation thereof

Abstract

Disclosed is a dispersion of fine particles of modified polyethylene, which comprises a hydrocarbon organic solvent and fine particles of an ethylene polymer or ethylene polymer composition dispersed in the solvent, wherein the ethylene polymer or ethylene polymer composition has an acid value of 0.3 to 75 mg-KOH/g as a whole and a crystallinity of at least 45% as determined by the X-ray diffractometry and has an average dispersed particle size of 0.3 to 20 mu m and a concentration of 15 to 60% by weight.

We claim: 
     
       1. A dispersion of fine particles of modified polyethylene, which comprises: (1) 80 to 100 parts by weight of a hydrocarbon organic solvent and fine particles of an ethylene polymer or ethylene polymer composition, and   (2) 0 to 25 parts by weight, based on the weight of the solvent and the polymer or polymer composition, of water, said fine particles being dispersed in the solvent and the water medium,   wherein the ethylene polymer or ethylene polymer composition is an organic acid graft-modified polymer or polymer composition having an acid value of 0.3 to 75 mg-KOH/g as a whole and having a crystallinity of at least 45% as determined by X-ray diffractometry, the particles having an average dispersed particle size of 0.3 to 20 μm, and the weight ratio of the particles to the hydrocarbon organic solvent is 100/60 to 100/600.   
     
     
       2. A dispersion as set forth in claim 1, wherein the ethylene polymer or ethylene polymer composition has an acid value of 1.5 to 30 mg-KOH/g as a whole and a crystallinity of at least 60%. 
     
     
       3. A dispersion as set forth in claim 1, wherein the dispersed particle size is 2 to 10 μm and the weight ratio of the particles to the hydrocarbon organic solvent is from 100/60 to 100/150. 
     
     
       4. A dispersion as set forth in claim 1, wherein the standard deviation value (δ) of the dispersed particle size is smaller than 5 μm. 
     
     
       5. A dispersion as set forth in claim 1, wherein the viscosity is 1 to 10,000 cP as determined by using a Brookfield type viscometer at a concentration of 40% by weight and a temperature of 25° C. 
     
     
       6. A dispersion as set forth in claim 5, wherein the viscosity is 20 to 1,000 cP. 
     
     
       7. A dispersion as set forth in claim 1, wherein the ethylene polymer is a carboxyl group-modified ethylene polymer in which an ethylenically unsaturated carboxylic acid or an anhydride thereof is included in the main chain or side chain of the polymer by graft copolymerization, block copolymerization or random copolymerization. 
     
     
       8. A dispersion as set forth in claim 1, wherein the ethylene polymer has an inherent viscosity (η) of 0.04 to 1 dl/g as measured in decalin as the solvent at 135° C. 
     
     
       9. A dispersion as set forth in claim 1, wherein the ethylene polymer is a polyethylene wax grafted with acrylic acid, methacrylic acid or maleic anhydride, which has an inherent viscosity (η) of 0.04 to 0.5 dl/g. 
     
     
       10. A dispersion as set forth in claim 1, wherein the ethylene polymer composition is a composition comprising (i) a carboxyl group-modified ethylene polymer in which an ethylenically unsaturated carboxylic acid or anhydride thereof is included in the main chain or side chain of the polymer by graft copolymerization, block copolymerization or random polymerization and (ii) an unmodified ethylene polymer at a weight ratio of from 1/99 to 50/50. 
     
     
       11. A dispersion as set forth in claim 10, wherein the ethylene polymer composition comprises the polymers (i) and (ii) at a weight ratio of from 3/97 to 20/80. 
     
     
       12. A dispersion as set forth in claim 10, wherein the ethylene polymer composition is a composition comprising (i) a polyethylene wax grafted with acrylic acid, methacrylic acid or maleic anhydride, which has an inherent viscosity (η) of 0.04 to 0.5 dl/g, and (ii) a polyethylene wax or ethylene/propylene copolymer wax having an inherent viscosity (η) of 0.08 to 0.5 dl/g and a density of 0.91 to 0.98 g/cc at a weight ratio of from 1/99 to 50/50. 
     
     
       13. A dispersion as set forth in claim 1, wherein the hydrocarbon organic solvent is an n-paraffin hydrocarbon solvent or an isoparaffin hydrocarbon solvent. 
     
     
       14. A process for the preparation of a dispersion of fine particles of modified polyethylene, which comprises adding an acid to an aqueous dispersion containing in the form of fine particles having an average dispersed particle size of 0.3 to 20 μm an ethylene polymer or ethylene polymer composition having an acid value of 0.3 to 75 mg-KOH/g as a whole and a crystallinity of at least 45% as determined by the X-ray diffractometry, in which at least a part of the carboxyl group corresponding to said acid value is neutralized with a basic substance, to agglomerate the fine particles, adding a hydrocarbon organic solvent to the agglomerate to transfer the fine particles into the solvent phase, and separating and removing the aqueous phase. 
     
     
       15. A preparation process according to claim 14, wherein at least 20% of the carboxyl group in the aqueous dispersion is neutralized with the basic substance. 
     
     
       16. A preparation process according to claim 14, wherein the acid is added to the aqueous dispersion so that the pH value of the aqueous phase is smaller than 6. 
     
     
       17. A preparation process according to claim 14, wherein the acid is added to the aqueous dispersion so that the pH value of the aqueous phase is 2 to 4. 
     
     
       18. A preparation process according to claim 14, wherein the acid is one forming a water-soluble salt by reaction with the basic substance. 
     
     
       19. A preparation process according to claim 14, wherein a surface active agent is added to the aqueous dispersion prior to the addition of the acid to the aqueous dispersion. 
     
     
       20. A preparation process according to claim 19, wherein the surface active agent is a nonionic surface active agent having an HLB value smaller than 12. 
     
     
       21. A preparation process according to claim 19, wherein the surface active agent is added in an amount of 0.1 to 10% by weight based on the ethylene polymer or ethylene polymer composition.